Energy Efficiency Standard for Social Housing: peer review

Case Study Group F

1. 1984-1991 mid floor flat, 60m ²
2. 1984-1991 mid terrace house, 76m ²
3. 1984-1991 semi-detached house, 74m ²

Case Study Group F: 1990 Baseline

Walls

• 1093 tenement dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1965 and 1990:
  • 95% of these featured cavity wall construction.
  • Almost half (47%) were noted to feature insulation to all external walls.
• 1210 mid-terrace, end-terrace and semi-detached dwellings were identified by the 1991 SHCS as belonging to the social housing sector and constructed between 1965 and 1990:
  • 578 of these were mid-terrace dwellings, of which 91% featured cavity wall construction.
  • 632 of these were end-terrace and semi-detached dwellings, of which 93% featured cavity wall construction.
  • 43% of the 1210 dwellings were noted to feature insulation to all external walls
• This SHCS age group spans 25 years, therefore for case study group 'F', describing the latter half of this period of construction, it is considered appropriate to assume wall insulation is present.
• The RdSAP methodology assumes a wall U-value of 0.35 W/m ².K for age band G filled cavity walls in Scotland (v9.90 and v9.91).

Ground Floor

• Where it is not possible to determine the level of floor insulation, the RdSAP methodology assumes a solid floor with no insulation for Scottish dwellings constructed between 1930 and 1991 ( RdSAP age bands C to G).
• For case studies 16 and 17 It has been assumed that some insulation is present calculated in the region of 0.30 W/m ².K and 0.36 W/m ².K respectively.
• Alternatively, table S11 and S12 in the RdSAP manual can be interpreted as indicating that no insulation would be present

Roof

• The majority of post 1965 mid-terrace houses from the social housing stock (87%), surveyed for the 1991 SHCS, featured a satisfactorily level of loft insulation, defined as 100mm in 1991. This has required further investigation to determine the validity of the baseline assumption, as discussed in Appendix E of the main report.

Glazing

• The majority of the 1093 social rented tenements, identified by the 1991 SHCS and constructed between 1965 and 1990, featured single glazing (63%), although 31% were noted to feature full double glazing.
• The majority of the 1210 social rented mid-terrace, end-terrace and semi-detached houses, identified by the 1991 SHCS and constructed between 1965 and 1990, featured single glazing (66%), although 26% were noted to feature full double glazing
• For this SHCS age group, the improved specification may be more predominant in construction occurring after 1983, therefore pre-2003 double glazing seems an appropriate 1990 baseline assumption for case study group F.

Ventilation: Chimneys

• The 1991 SHCS indicates that only 11% of social rented tenements, and 30% of social rented houses (mid-terrace, end-terrace and semi-detached only), constructed between 1965 and 1990, featured a gas or solid fuel fire, therefore the assumption of 'no open chimneys' is considered appropriate.

Space and water heating

• Case study group F specifies factory applied foam insulation thickness of 25mm for the hot water cylinder. This corresponds to the default performance assumed by RdSAP for hot water cylinders in Scottish dwellings constructed between 1984 and 1991.

Electric heated dwellings
Space and water heating

• Based on observations from the 1991 SHCS:
  • 78% of electric heated, social rented tenement dwellings, constructed between 1965 and 1991, featured storage heaters and 90% used electric immersion to provide hot water.
  • 74% of electric heated, social rented mid-terrace, end-terrace and semi-detached houses, constructed between 1965 and 1991, featured storage heaters and 88% used electric immersion to provide hot water
• The 1990 baseline assumptions correspond with the above observations.

Gas heated dwellings
Space and water heating

• It is unlikely that data will be available describing the efficiency of the boiler installed in the 1990 property, therefore it will be necessary to refer to the assumptions detailed within the SAP methodology: Appendix S assumes pre 1998 gas boilers are not fan-assisted, which corresponds to an efficiency of 66% (with the exception of a regular floor mounted boiler installed pre 1979 with an assumed efficiency of 56%).
• Should any of the efficiency adjustments outlined in Table 4c of the SAP methodology be applicable, the boiler efficiency may be reduced by 5%. This means a regular, non-condensing, pre-1998 gas boiler (not fan assisted) without any thermostatic control of room temperature will be assumed to have an overall efficiency of 61%.

Recommendations:

• Reference should be made to Appendix E of the main report in relation to the 1990 baseline assumption for loft insulation.
• The minimum efficiency assumed for the boiler winter seasonal efficiency (applied for the space heating requirement) should be no less than 61%.
• For the baseline it would justifiable to model the ground floor properties F16 and F17 without floor insulation, utilising RdSAPs basic assumptions.

Case Study Group F: SHQS 2015

• The case studies feature 25mm of factory applied foam insulation to the hot water tank. As long as the pipes are insulated, or contribute to the space heating requirement, case study group F complies with element 33 of Annex C.
• Sub-elements 34A and 34B require that the property features a full central heating system addressing all habitable rooms (excluding the kitchen and bathroom), and that it is deemed efficient. Both the storage heaters and gas boiler specified for the baseline property meet the necessary criteria
• The 1990 baseline versions of case study 15, and gas heated case studies 16G and 17G, exceed the minimum SAP rating to meet compliance with Element 35 of Annex C. No additional measures are considered for these dwellings under this stage of improvements.

Electric heated dwellings
Roof

• To exceed the minimum SAP rating, in line with element 35 of Annex C, it is necessary to increase the loft insulation thickness to 250mm for case studies 16E and 17E.

Space and water heating

• Free-standing large volume electric storage systems (associated with case study 17E only) may be deemed efficient as long as they were installed after 1984, however it may be necessary to upgrade to an improved system to help exceed the minimum SAP rating for element 35 of Annex C
• The proposed fan storage heaters specified for case studies 16E and 17E will have the same efficiency as the older storage systems, but will benefit from increased 'responsiveness' ^[17] and automatic controls, contributing to a reduction in the space heating requirement, and consequently an improved SAP rating.
• The improvement to the hot water tank insulation for 16E and 17E, increasing the factory applied foam insulation thickness from 25mm to 80mm, identifies another method by which landlords can reduce the hot water energy consumption, CO ₂ emissions and consequently SAP rating.

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology is specified for case study 17E, however this will only be suitable for a limited number of properties, where they meet sufficient criteria to ensure the effective operation of the technology ( e.g. suitable orientation, sufficient space on the roof, optimal angle of roof, minimal over shading).
• Should optimal conditions associated with any of the above criteria not be met, additional costs may be incurred to try optimise operational conditions ( e.g. investment in a supporting frame to improve the tilt angle, or multiple inverters to minimise the impact of partial shading for periods of the day).

Recommendations:

• Alternative technologies (such as improved glazing) should be considered to help case study 17E achieve the minimum SAP rating for the SHQS over solar PV, where the suitability of this technology is limited in relation to a number of building specific characteristics.

Case Study Group F: Further Measures 2020

• The EESSH outlines a minimum EI rating to be achieved for electric fuelled properties and gas fuelled properties. These are:
  • C (70) and C (80) respectively for a mid-floor flat,
  • D (55) and C (70) respectively for a mid-terrace house, and
  • E (50) and D (65) respectively for an end-terrace/semi-detached house.
• Case study 16E has exceeded the minimum EI rating based on the measures specified for the SHQS 2015 improvement stage, therefore no additional measures are considered.
• Case study 17E just falls short of the minimum EI rating, therefore does not meet compliance with the EESSH until application of the 'advanced measures 2050'.

Electric heated dwellings
Glazing

• Case study 17E specifies post-2003 double glazing under the 'further measures 2020 stage, but still just falls short of the minimum EI rating to meet compliance with the EESSH. Additional measures should be suggested to try help meet compliance.

Space and water heating

• The proposed fan storage heater (for case study 15E only) will have the same efficiency as the older system, but will benefit from increased 'responsiveness' ^[18] and automatic controls, contributing to reduced space heating requirements, fuel costs and consequently a better SAP rating.
• The improvement to the hot water tank insulation (for case study 15E only), increasing the factory applied foam insulation thickness from 25mm to 80mm, identifies additional efforts landlords can implement to help realise a better SAP rating.

Gas heated dwellings
Roof

• Where not previously improved upon, the loft insulation thickness has been increased to 250mm for case studies 16G and 17G, to help improve the EI rating associated with the dwelling.

Glazing

• All the gas heated case studies in group F specify the installation of post-2003 glazing for the 'further measures 2020' improvement stage, in an effort to help exceed the minimum EI rating.

Space and water heating

• The indicative life expectancy for a condensing boiler is in the region of 15 years ^[19] , therefore installation of a new system is appropriate for both the ' SHQS 2015' or 'Further Measures 2020' improvement stages. This also provides an opportunity to upgrade the control strategy.
• Table 4b of the SAP methodology specifies a non-condensing combi-boiler to have an efficiency of 70-74%. Any installations after 2005 will be condensing systems, thus assume an efficiency of 80-84%. The case study control specification indicates that the system does not qualify for any efficiency adjustments detailed in table 4c of the SAP methodology.
• Improved boiler efficiency will yield considerable space heating and hot water energy reductions. Standard 6.3 of the Domestic Technical Handbook specifies a minimum seasonal efficiency of 88% ( SEDBUK 2009) for gas boilers. It is proposed that this value is used to describe the efficiency for any future installations, where it represents the current minimum standards.
• A more efficient boiler will use less energy to address the load on the heating system. Any savings realised by a measure which reduces the load on the heating system will be greater under the operation of a less efficient boiler compared to a more efficient system. This is important to bear in mind when considering the cumulative effect of implementing energy efficiency measures installed over a number of stages: the benefits of individual measures cannot be added together.

Recommendations:

• Additional improvement measures should be suggested for case study 17E to ensure it can achieve the minimum EI rating for the EESSH.
• An assumed gas boiler efficiency of 88% is proposed in line with the minimum standards outlined by Standard 6.3 of the Domestic Technical Handbook.
• Social landlords should be reminded that the case studies demonstrate the cumulative application of efficiency measures over three stages, and the potential benefits realised by a single measure are subject to change in relation to the other measures in place.

Case Study Group F: Advanced Measures 2050

Renewables: Solar PVs to 20% of roof or 3m ² of solar thermal

• Solar technologies, specified for case studies 16 and 17, will only be suitable for a limited number of properties, where they meet sufficient criteria to ensure the effective operation of the technology ( e.g. suitable orientation, sufficient space on the roof, optimal angle of roof, minimal over shading).
• Should optimal conditions associated with any of the above criteria not be met, additional costs may be incurred to try optimise operational conditions ( e.g. investment in a supporting frame to improve the tilt angle, or multiple inverters to minimise the impact of partial shading for periods of the day).

Electric heated dwellings
Walls

• Assuming cavity wall construction, the filled cavity U-value for construction built in Scotland between 1984 and 1991 is 0.35 W/m ².K.

Glazing

• Upgrading the glazing specification to post-2003 double glazing allows landlords to view the potential benefits from this measure. It is more suited to an 'advanced measure' where it may not be necessary to replace the pre-2003 double glazing for a number of years.

Recommendations:

• There are no recommended changes to the assumptions specified for the 'Advanced Measures 2050' improvement stage, for case study group F.